Specifically on oil productions platforms and in industrial plants where hydrocarbon is handled and processed, it is important to be able as soon as possible to detect the existence of combustible gases which are leaking. In fact, more than fifty percent of gas leaks recurring on oil platforms are today detected manually. Such detection is of an incidental type and shows that there is a need for installation of more gas detectors. Gas detectors to be used on oil platforms have to fulfill stringent technical requirements. They have to be extremely reliable, sensible, EX approved and must be able to exist in harsh weather conditions over time. High technology equipment exist which can fulfill the requirements, but for extremely high price per detector and with considerable installation costs, among others because they have to be linked with fixed wiring to a central. This limits coverage of an area. Cheaper gas detector types are desirable.
It is thus an advantage that the detector arrangement is of wireless type, specifically because of the installation costs. Then it is at a same time of interest to use separate power supply for each detector arrangement, e.g. a battery supply. But it is at the same time necessary that the detector is “ON” continuously and conventional gas detectors typically draw so much current that battery operation becomes impractical or impossible.
Specifically advantageous are gas detectors of the type which are able to perform a precise determination of the concentration of a specific gas type, e.g. detector for methane have a considerable higher energy consumption than a more “unspecific” detector which can detect changes in a gas mixture, but can not determine for sure which gas has been added to the mixture.
(Examples for unspecific detector types are acoustical sensors with electrostatic, electromagnetic or piezo-electrical activation. Examples for specific detector types are photo acoustical sensors and other infrared sensors which can be made specific for e.g. methane, C3H8, CO2, natural gas).
Other areas of interest with respect to disposal of the gas detector are limited areas within a manhole or tanks on vessels and down in mines lacking electricity and data communication and where one can not have fixed detector installations.
There is thus a need for a detector which both are really energy efficient and which gives good measurements of the specific gases which are considered to be dangerous in a given area.
An example of prior art is disclosed in the Patent Application EP 1 316 799 A2, where a gas detector for a specific gas is used to control a ventilation system. This publication relates mostly to algorithm for calculation of threshold values for activation.
The International Patent Application WO 00/16091 A1 describes a gas sensor group for a number of specific gases where control devices for the single gas sensors are powered down and up by a multiplexer to avoid crosstalk of signals from single sensors.
The Patent Applications US-2004065140 A1, GB-2364807 A, JP-2002109656 A and U.S. Pat. No. 6,321,588 B1 show systems and methods used to monitor changes in gas concentrations or gas leaks at hardly accessible places in industrial plants. These comprise at least one sensor and energy saving methods by sensors and other components being able to be powered down or the use of pulsed batteries.
These examples of prior art in the field do not solve the problem which is described above. The present invention seeks to satisfy the above mentioned need for reasonably priced and energy efficient gas detectors.